1. Field of the Invention
The present invention relates to a bonding structure of optical members wherein respective optical axes of a plurality of the optical members such as a laser diode and an optical waveguide substrate are optically aligned with each other with an accuracy of sub-microns while support members supporting the optical members are bonded.
2. Description of Related Art
As to a light source for a blue laser used for an optical pickup and so on, a second harmonic generation (SHG) device of a quasi phase matched (QPM) type using an optical waveguide, in which a periodical polarization reversal construction is formed on a single crystal of lithium niobate or lithium tantalite, is expected.
In order to manufacture such a device mentioned above, it is necessary to fix the optical waveguide substrate, on which the polarization reversal construction is formed, and a laser diode to a support member, and align an optical axis of the optical waveguide and an optical axis of laser diode with each other with an accuracy of sub-microns. In this case, generally, the optical waveguide substrate is bonded to a surface of the support member by means of an optical adhesive, and the optical adhesive is hardened. In addition, it is necessary to bond a support member supporting the laser diode to the support member supporting the optical waveguide substrate. In this case, use may be made of a resin of ultraviolet ray hardening type, a resin of visible ray hardening type, and an instant adhesive.
However, it is very difficult on an actual manufacturing to align optically the optical axes of the optical waveguide and the laser diode with an accuracy of sub-microns while the optical adhesive is hardened. In order to align the optical axes accurately, it is necessary to harden the adhesive arranged between the two support members just after the optical axes of the laser conductor and the optical waveguide are aligned accurately with an accuracy of sub-microns. Moreover, it is necessary to harden the adhesive after the two support members are bonded. In addition, since the optical member must have generally reliability at a wide temperature range such as from xe2x88x9240xc2x0 C. to +80xc2x0 C., it is necessary to endure a heat cycle under such a temperature range. Particularly, almost all surface of the support member supporting the laser diode is coated by a gold plating film. In this case, since a surface of the gold film is inactive, it is difficult to bond.
The inventors inspected the bonding structures using various kinds of resin adhesives. As a result, it was founded that a high strength bonding was obtained with respect to a surface particularly a gold plated surface of the support member by using an acrylic resin adhesive. However, even in the case that the two support members were bonded by using the acrylic resin adhesive, it was observed that an optical coupling loss between the laser diode and the optical waveguide was increased after a heat cycle test.
An object of the present invention is to provide a bonding structure of optical members having a first optical member, a second optical member, a first support member supporting the first optical member, and a second support member supporting the second optical member, wherein the first support member is bonded to the second support member, which can obtain a sufficient bonding strength between the support members and can suppress an increase of an optical coupling loss after applying a heat cycle or a thermal shock thereto.
According to the present invention, a bonding structure of optical members having a first optical member, a second optical member, a first support member supporting the first optical member, and a second support member supporting the second optical member, wherein the first support member is bonded to the second support member, comprises a construction such that:
(1) the first support member and the second support member are bonded with each other via a hardened acrylic resin adhesive under a condition such that an optical axis of the first optical member and an optical axis of the second optical member are optically aligned with each other with an accuracy of within 1 xcexcm; and
(2) a viscosity of the acrylic resin adhesive before hardening is larger than 500 cP and lower than 5000 cP.